Page 128 - Numerical Analysis and Modelling in Geomechanics
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STABILITY OF UNSATURATED SOIL SLOPES 109
Figure 4.2 Volumetric water content vs pore water pressure.
the pore water pressure. At 100% saturation, the volumetric water content is
equivalent to the soil porosity.
In unsaturated flow, the hydraulic conductivity is highly dependent on the
water content of a soil. This is because of the heterogeneous volume distribution
of the pore water (or water content or matrix suction) within the soil mass. It is
generally assumed that water flows along a web of interconnected but continuous
conduits, and that as the water content increases, the size and number of conduits
increase, thereby enhancing the capability to conduct water through the soil.
Since a unique relationship is assumed between the water content and pore water
pressure, the hydraulic conductivity is thus also a function of pore water pressure
as shown in Figure 4.3.
For an isotropic unsaturated soil element, the constitutive equation for the
water phase (Lam et al. [12]) is:
(4.6)
where m and m can be regarded as constants for a particular time step during a
w
a
transient process. Under saturated conditions, m is equivalent to the conventional
a
